THE NERVOUS SYSTEM OF THYSANURA. 



William A. Hilton. 

 (Department of Zoology, Pomona College, Claremont, California). 



The central ganglia of representative genera, Campodea, 

 Evalljapax, Lepisma and Machilis were examined. 



The first important papers dealing with any of these genera 

 were those of Grassi 1885 and 1888. In both of these, brief 

 discussions of the nervous system are given, but no clear picture 

 of the complete nervous system. Probably the most copied 

 figure of the nervous system of any thysanuran is the one of 

 Gudemans, 1887. In this, a drawing of the complete nervous 

 system of MachiHs is given which could hardly be improved 

 upon, bu^ the position of the optic lobes, brain and other 

 cephalic parts are not shown in the relations we find them 

 within the body of the animal. In this figure there is a rep- 

 resentation of the fine medial nerve. Another paper by Grassi 

 in 1888 shows the general form of the nervous system of 

 Campodea and Japax and a number of details are clearly given. 

 Bottger, 1910, on Lepisma saccharina L. gives a very complete 

 account of the brain and shows it to be very nearly as complex 

 as that of other insects. 



Campodea undoubtedly has the most primitive, or at least, 

 the simplest nervous system of any of these insects. The brain 

 is provided with antennal nerves well towards the forward end. 

 The first ventral ganglion is nearly under the brain, then there 

 follow three large thoracic ganglia and seven small abdominal 

 gangHa with the last one a little larger than the rest. This 

 corresponds to Grassi's figure, but this one gives greater detail. 

 It was drawn from gross dissection. No frontal ganglion is 

 shown as one was not clearly recognized in section or dissection. 

 (Figure 1). 



Japax or Evalljapax in this case, differs quite a little from 

 Campodea in appearance, the brain is of different shape, and 

 as it is also without eyes, the forward antennal nerves are the 

 most marked. The ventral ganglia are a little more oval, 

 branches are more prominent and there is one more abdominal 

 ganglion. The last abdominal as in Campodea, is a little larger 



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